The present invention pertains to a connection of two spring ends of a spring strand such as in particular of a garter spring or an annular spring strand in the form of, for example, a miniature annular ring with canted windings or a miniature garter spring. The present invention also pertains to a method for connecting two spring ends and to the production of an annular spring with canted windings or of a garter spring, especially of the miniature type.
Such annular spring strands are known as hose springs or annular spring strands with canted windings. They are also known as so-called “garter springs” or “canted coil springs”. Such springs are used, for example, for seals, electrical contacts, and mechanical plug-in connections.
The two ends of an individual spring strand are usually connected positively to each other to form the garter spring by providing one end with a smaller diameter and by screwing it into the other end. Garter springs of this type are described in, for example, U.S. Pat. No. 2,530,163, U.S. Pat. No. 3,186,701, and U.S. Pat. No. 4,880,217. A disadvantage is that these screwed connections lead to a considerable stiffening of the spring, extending over several windings. Especially in the case of very small garter springs, this stiffening has a negative effect.
As a rule, the two ends of a canted coil spring are connected to each other by welding. Such canted coil springs are described in, for example, US 2004/0245686 and in US 2010/0090379. The manner in which the connection is formed is not described in detail but rather merely indicated as a point in the figure without any detailed explanation. Both patent documents describe only positive types of connections. In U.S. Pat. No. 3,323,785, the connection of the two ends is expressed by the words “formed into an annulus by suitably attaching the opposite ends of the spring to each other”, but the document does not go into any further detail. U.S. Pat. No. 3,468,527 states that the ends are welded together but does not give a detailed description of how this welding must be done and what form it should take (“the ends joined together by welding to form a unitary annulus”).
In addition to the materially bonded connection of the two ends of a canted coil spring, positive-locking connections with specially configured shapes at the ends are also known, such as those described in US 2004/0245686. These suffer from the disadvantage that they cause a change in the stiffness of the spring in the area of the connection, which can have disadvantageous effects on the function of the spring.
End windings resting against each other in the circumferential direction can also lead to an unallowably large reduction in the spring travel of the spring in the area of the connection. This means that a canted coil spring can be compressed to a lesser degree in the connection area than in the rest of the spring and is thus unable to function to it full extent.
The fine positioning of the two spring ends with respect to each other is another problem which has not so far been solved satisfactorily in the production of these connections, especially in the case of very small garter springs and coil springs with or without canted coils. In the case of very small garter springs and spring strands with or without canted coils, the correct positioning of the two ends with respect to each other is very difficult, both with respect to the centering of the two ends on each other and also with respect to the position in the circumferential direction required to prevent an air gap between the two ends.